Protection of header surfaces



' Fig. 2

INVENTORZ Ernsf Krelselmaler Attorn y I BY June 10, 1969 E. KREISELMAIER PROTECTION OF HEADER sunmcss Filed Marqh 16, 1967 United States Patent 3,448,804 PROTECTION OF HEADER SURFACES Ernst Kreiselmaier, Luggendelle 17, Gelsenkirchen-Buer, Germany Filed Mar. 16, 1967, Ser. No. 623,719 Claims priority, applitigtitsm Sgermany, Mar. 19, 1966, 3

Int. Cl. F28f i9/o2, 13/18 US. Cl. 165-133 6 Claims ABSTRACT OF THE DISCLOSURE My present invention relates to an assembly of the type wherein a metal plate is penetrated by one or more metallic tubes, e.g. which form a header as used in boilers, condensers and other heat exchangers.

In such installations the header plate usually consists of iron while the tubes are made from copper or brass. In assemblying these elements, the tube ends are inserted with slight clearing into perforations of the plate and are then expanded by rolling to form a tight junction. Upon prolonged use, however, the joints between the plate and the tubes do not remain fluidtight, owing to differences in the thermal coefficients of expansion and to the formation of couples between the different metals leading to electrochemical erosion. The resulting leakage is highly objectionable, particularly in condensers and other heat exchangers where it permits the intrusion of brine or other fluids into the medium whose temperature is to be controlled.

Prior attempts to remedy this situation with the aid of a protective resinous coating on the header plate have been only partly successful. In particular, the liquid conveyed through the tubes still had a tendency to penetrate between the layer and the metallic structure with resulting erosion of the joints.

The general object of my present invention, therefore, is to provide an improved assembly of this description which, without resorting to more expensive metals or alloys, avoids the disadvantages set forth above, along with a process for producing such an assembly.

I have found that the chief cause of fluid penetration between a metallic header structure and a protective layer lies in the existence of turbulent flow at the tube entrances, this flow beingdue to the cylindrical shape of the tube and of the corresponding hole in the protective layer which causes an abrupt change in flow direction between the tube and the fluid path across the plate surface. This turbulence can be suppressed, in accordance with an important feature of my invention, by an outward flaring of the perforations of the protective layer which give access to the respective tube ends, advantageously in such a manner that the minimum diameter of these perforations equals the inner diameter of the tube ends so that the tube wall is faired into the wall of the hole.

To produce a layer so perforated, in accordance with another feature of my invention, I temporarily plug each tube end with a removable stopper having an outwardly ice diverging frustoconical part projecting from the tube end and, therefore, beyond the plate surface; after the p otective layer has been cast onto the plate surface or otherwise applied thereto, and after a sufficient hardening period, if necessary, the stoppers are withdrawn so as to leave frustoconical holes in the layer which register with the tube ends in the aforedescribed manner. To facilitate such withdrawal, the layer should surround the stoppers in a nonadhering manner; if needed, therefore, an antibonding agent (e.g. silicone oil) may be applied to the projecting heads of the stoppers before the resinous mass is applied to the plate surface.

The invention will be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 is a cross-sectional view of a header assembly of conventional construction;

FIG. 2 is an enlarged cross-sectional view of part of the assembly of FIG. 1 with stoppers inserted preparatorily to application of a protective coating in accordance with the invention;

FIG. 3 is a view similar to FIG. 2, showing the coating applied; and

FIG. 4 is another view similar to FIG. 2, illustrating the finished layer upon removal of the stoppers.

In FIG. 1 I have shown a header comprising a metal plate 1, e.g. of cast iron, penetrated by the ends of a bank of tubes 2, e.g. of brass. Owing to prolonged use, crevices 3 have begun to form at the junctions between the tubes and the plate.

As shown in FIG. 2, a series of stoppers 4 are removably inserted into the ends of tubes 2, each of these stoppers having an outwardly diverging frustoconical head 5 projecting beyond the surface of plate 1. According to FIG. 3, a layer '6 of protective plastic material (e.g. an epoxy resin) is cast onto plate 1 and around the heads 5 of stoppers 4, this layer also penetrating into the crevices 3 which have developed between the plate and the tubes 2. The stoppers 4, consisting for example of Teflon, are thereafter removed to leave the layer 6 with frustoconical holes 7 which are faired into the inner wall surfaces of the corresponding tubes 2 and are flared outwardly, at an angle determined by the vertex a (FIG. 3) of the frustoconical heads 5, to facilitate the passage of fluid into and out of the tubes 2 without substantial turbulence; this vertex angle may range, for example, between 45 and It will be noted that the tube ends overlain by the layer 6 all terminate at a common level L (FIG. 4) substantially coinciding with the partly eroded upper surface of plate 1, this level also constituting the plane of contact between the tube ends and the protective layer.

I will be apparent that the process described in connection with FIGS. 24 can be utilized on existing headers or carried out directly at the assembly plant. In the former case, the condenser or other installation need not be completely taken out of service if only some of the tubes 2 (e.g. half of the bank illustrated in FIG. 1) are plugged at one time and upon removal of the stoppers from the layer applied to the corresponding surface portion of plate 1, the remainder of the assembly is similarly treated.

I claim:

1. An assembly comprising a metal plate and a metallic tube provided with an end penetrating said plate and opening onto a surface thereof, said end lying substantially at the level of said surface, and a layer of a protective plastic material adhering to said surface while overlying said end, said layer having a hole which registers with said end and is bounded by an outwardly diverging peripheral wall, said plate being formed along said surface with crevices at the junctions of said plate with said tubes, said layer filling said crevices.

2. An assembly as defined in claim 1 wherein the minimum diameter of said hole equals the inner tube diameter at said tube end.

3. An assembly comprising a plate and open-ended tube means penetrating said plate and opening onto a surface thereof substantially at the level of said surface, stopper means adapted to be removably insertable into said tube means and diverging frustoconically therefrom beyond said surface upon such insertion, and a layer of a protective material adhering to said surface and overlying said tube means while surrounding the projecting part of said stopper means in nonadherent relationship therewith whereby said stopper means can be removed to expose said tube means.

4. An assembly as defined in claim 3 wherein said plate is metallic, said layer is resinous and said tube means comprises a bank of metal tubes extending substantially at right angles to said plate on the side thereof opposite said surface.

5. An assembly comprising a metal plate and a band of metallic tubes penetrating said plate and opening onto a surface thereof, said tubes having coplanar ends substantially flush with said surface, and a layer of a protective plastic material adhering to said surface while overlying said coplanar ends along a plane of contact substantially coinciding with said surface, said layer having perforations which register with said ends and whose diameters correspond to the inner tube diameters at said plane of contact, said plate being formed along said surface with crevices at the junctions of said plate with said tubes, said layer filling said crevices.

6. An assembly as defined in claim 5 wherein said perforations diverge outwardly from said plane of contact.

References Cited UNITED STATES PATENTS 2,225,615 12/1940 Bay 165-433 2,303,416 12/1942 Woods l65178 3,326,279 6/1967 Eisberg et al 165134 3,270,114 8/1966 Westlake 264259 ROBERT A. OLEARY, Primary Examiner.

THEOPHIL W. STREULE, Assistant Examiner.

US. Cl. X.R. 165l78 

